【摘要】 利用NCEP/NCAR逐日再分析资料和地面观测资料,对比分析了2018年1月江淮地区两次持续性强降雪过程的大气环流,研究了中高、低纬度系统(阻塞高压和南支槽)在持续性强降雪过程中的协同作用,探讨了阻高指数和南支槽指数正负位相的低频波动对中长期预报的可参考性。结果表明:(1)两次强降雪过程发生时大气环流持续异常,极涡呈"偶极型",中高纬度阻塞形势明显,地面冷高压强大,有利于强冷空气南下;低纬度副高、南支槽维持,有利于暖湿气流向江淮地区输送;冷暖空气交汇,出现明显的中高、低纬度系统协同作用;(2)强降雪过程主要是由中高纬度系统尤其是阻塞高压稳定维持和低纬度的南支槽相互配合造成的,两次过程均发生在阻高偏强、南支槽偏强且位势高度峰区和谷区相叠加的时间段;(3)两次持续性强降雪过程中,极涡位置、阻高和南支槽强度以及低层水汽条件、垂直环流等方面存在一定的差异,使得两次过程的降雪范围、强度和类型具有不同特点;(4)阻高异常偏强(弱)或南支槽异常偏强(弱)有(不)利于持续性降雪过程发生;持续性强降雪发生时阻高和南支槽的差值指数(UI-STI)具有明显异常偏高的特征,对强降雪过程预报具有一定的指示意义;(5)阻高和南支槽指数具有显著的10～30天低频变化特征,其正负位相的低频波动可提前两周以上,为强降雪过程预报提供参考。更多还原

【Abstract】 Based on the surface observation data and NCEP/NCAR daily reanalysis data,the atmospheric circulation of the two persistent heavy snow processes over Yangtze and Huaihe River Valleys in January 2018 were analyzed,and the impact of synoptic system and low-frequency variation in high and low latitudes( Ural block high and southern branch trough) on persistent heavy snow processes were discussed. Results are shown as follows:( 1) The two processes happened with persistent atmospheric circulation anomalies,for example,the polar vortex had a dipole-type distribution,and the blocking high pressure was steady and strong in middle-high latitudes,with cold high pressure over the plain,thus in favor of the southward advance of cold air. In lower latitude,the west Pacific subtropical high and southern branch trough were stable,which is very favorite to transportation of heat and moisture to Yangtze and Huaihe River valleys. Cold air from north and warm-mosit air from south converged to each other and then the favorite environment of heavy snow could appear.( 2) The stable and strong Ural block high and the southern branch trough and their interaction played an important role in the two processes.( 3) There were differences of the polar vortex、blocking high、southern branch trough、low-level moisture and vertical circulation between the two processes,leading to different features on snow area、intensity and type.( 4) Stronger blocking high and deeper southern branch trough benefit the occurrence of persistent heavy snow. The variation between the index of blocking high and southern branch trough was high in those strong snow days,which had important implications for middle and long term forecast on persistent heavy snow.( 5) The low-frequency oscillation period of 10 ～ 30 days was the most remarkable component of blocking high and southern branch trough and gave a good reference on weather forecast over two weeks.更多还原